The present invention relates to a semiconductor laser and a method for fabricating the same, and more particularly to a compound semiconductor laser having an improved carrier injection structure for injecting carriers to multiple quantum well layers and a method for fabricating the same.
There has been known various conventional vertical carrier injection multiple quantum well laser device, wherein carriers, for example electrons and holes are injected into a multiple quantum well active layer in a direction vertical to a surface of the multiple quantum well active layer. FIG, 1 illustrates energy band gap profiles. FIG. 2 illustrates electron and hole densities in individual quantum well layers. Since electrons have a small effective mass whilst holes have a larger effective mass and further electrons and holes are pulled to each other by, coulomb force, both the electron and hole densities are high in a quantum well layer near the p-side electrode and they are low in a quantum well layer near the n-side electrode. FIG. 2 shows a large difference of each of the electron and holes densities in individual quantum well layers. This large difference prevents increasing the number of multiple quantum well layers, thereby resulting in a difficulty in obtaining a high gain of power. This is disclosed in N. Tessler et pal. 13th IEEE Semicon. Laser Conf. 1992 D5, 44.